Background and Purpose— The role of hypercoagulable states in the pathogenesis of ischemic stroke in black subjects is not known, and data on normal reference ranges in black populations are lacking. This study estimated ethnic-specific reference ranges in a community population to determine the prevalence of thrombophilic states in a multiethnic stroke population. Methods— Free protein S, protein C, antithrombin III, activated protein C resistance, IgG anticardiolipin antibodies, and lupus anticoagulant were determined in 130 consecutive ischemic stroke cases ≤65 years of age (50 black Caribbeans, 30 black Africans, 50 whites) and 130 community controls. Results— Black African controls had significantly lower protein S (P<0.001) and protein C (P=0.049) and a trend toward lower antithrombin III (P=0.056) levels compared with white controls. Black Caribbean and African controls had higher diluted …